Methods are being developed and tested to detect and quantify oxidative damage to DNA in non-dividing cells in order to determine whether hydroxyl radicals generated either by redox cycling a toxin utilizing endogenous enzymes, or as a result of metabolism which has been activated by a toxin, may be involved in the pathogenesis of neurodegenerative disorders. Oxidative damage to neuronal DNA could result in impaired neuronal function if the damage remained unrepaired and accumulated. In order to measure DNA damage , either neuronal or mitochondrial, gas chromatographic and liquid chromatographic mass spectrometric methods are being developed to detect and quantify a variety of nucleosides. Assays for non-nucleoside biomarkers of oxidative processes, such as kynurenine from tryptophan are also being developed. The release of diffusable, soluble neurotoxins and growth controlling factors by activated macrophages/microglia has been reported following chronic HIV infection and various types of brain injury. A cultured neuronal cell bioassay from fetal rat has been devised and tested for quantitative responses to monitor the isolation and characterization of soluble factors isolated from conditioned media supporting activated macrophages or HIV- infected macrophages. Extracts of conditioned media are being separated into component classes (lipids vs. non-lipids, low vis high molecular weight) in order to guide separations using bioassay responses).